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Starting a Predicta Princess restoration but want to get it working first - Printable Version

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Starting a Predicta Princess restoration but want to get it working first - apERNA1985 - 02-12-2022

I have a Predicta Princess that has been sitting since 1977. It's in unbelievable original condition. I'd like to get it working before recapping it. I think my previous trouble with my Tandem was changing everything at once, I'd like to try doing a little at a time so I know where to look when something goes south.  replaced the main filter caps hoping it would work, the Damper, horizontal output, and High Voltage rectifier tubes don't have heater voltage. It looks like one side goes to ground, but on the Sams they just put an X on the other leg. What does the X mean?

RE: Starting a Predicta Princess restoration but want to get it working first - morzh - 02-12-2022

I am a storng proponent of recapping prior to atttempting to "get it working". For everything, TVs included.

RE: Starting a Predicta Princess restoration but want to get it working first - RodB - 02-12-2022

The X usually means that all Xs are connected, in this case probably one of the power transformer secondary windings. It will also have an X.

RE: Starting a Predicta Princess restoration but want to get it working first - MrFixr55 - 02-13-2022

In almost any post-war TV I ever worked on, the HV Rectifier gets its power from a few turns of very well insulated wire around the frame of the flyback acting as a secondary. Is this a transformer powered set or are the tube heaters in series? If parallel and transformer powered (and based on the tube layout in RadioMuseum, it appears so), and if the damper and Horizontal Output Tubes are mounted on the PC instead of the chassis frame, look for a poor solder joint on any of the posts bent up from the metal chassis frame that support the PC Board. Often there is not a continuous ground plane on the PCB, and they rely on the individual posts for ground connections. I have fixed several RCA B/W and color TVs from the 50s to early 60s in my youth that had this condition.

RE: Starting a Predicta Princess restoration but want to get it working first - apERNA1985 - 02-13-2022

It maybe a circuit board issue because the heater is lit on 6AW8A.

Here is the schematic

RE: Starting a Predicta Princess restoration but want to get it working first - MrFixr55 - 02-13-2022

Gotta go back to work. Are the Hor Output and Damper on the PCB? Looking at the schematic, one heater connection has the "X"X the other is chassis ground. If these tubes are on the PCB, really smells like the cold solder joint on the chassis post issue. Solder a wire to the appropriate socket connection on both tubes and find a good tang to solder it to nearby on the chassis. It will strengthen the connection. It is likely that these 2 tubes draw the most heater current of all the tubes in the set. I wouldn't be surprised if this is the issue that put the set out to pasture in the first place.

RE: Starting a Predicta Princess restoration but want to get it working first - Bob Andersen - 02-13-2022

Yes, they are on the main PCB. I had the same issue with the damper tube on the model. It turned out to be a cold solder join on the grounding stake nearest that tube.

RE: Starting a Predicta Princess restoration but want to get it working first - apERNA1985 - 02-13-2022

I like that this set isn't series string. I was able to pull the tubes one at a time and I don't have any heater voltage. Oddly enough I have the same issue on my Debutant. I'm hoping to track down where the break in the circuit is. I thought it was going to be a bad ground to.